New micropalaeontological studies on the type section of the Campanian-Maastrichtian at Tercis (SW France): new ostracodes obtained using acetolysis Bernard Andreu, Gilles Serge Odin To cite this version: Bernard Andreu, Gilles Serge Odin. New micropalaeontological studies on the type section of the Campanian-Maastrichtian at Tercis (SW France): new ostracodes obtained using acetolysis. Carnets de Geologie, Carnets de Geologie, 2008, CG2008 (A02), pp.1-14. hal-00235838v2 HAL Id: hal-00235838 https://hal.archives-ouvertes.fr/hal-00235838v2 Submitted on 21 Mar 2008 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Carnets de Géologie / Notebooks on Geology - Article 2008/02 (CG2008_A02) New micropalaeontological studies on the type section of the Campanian-Maastrichtian at Tercis (SW France): new ostracodes obtained using acetolysis 1 Bernard ANDREU 2 Gilles Serge ODIN Abstract: Through the use of acetolysis new micropalaeontological studies on the type section of the Campanian-Maastrichtian boundary at Tercis (SW France) we obtained additional information on ostracodes. Acetolysis on hard carbonates levels of the Tercis quarry found 22 species in addition to those of the studies published in 2001. Today, 75 species are recognized: they represent 34 known genera, and 4 currently unidentified. Small species usually rare of the genera Aversovalva, Bythoceratina and Eucytherura were collected. All of the assemblages (of both genera and species) are characteristic of a Campanian-Maastrichtian open carbonate platform environment. Key Words: Ostracodes; Campanian; Maastrichtian; stratotype; Tercis; Aquitaine; France; acetolysis. Citation : ANDREU B. & ODIN G.S. (2008).- New micropalaeontological studies on the type section of the Campanian-Maastrichtian at Tercis (SW France): new ostracodes obtained using acetolysis.- Carnets de Géologie / Notebooks on Geology, Brest, Article 2008/02 (CG2008_A02) Résumé : Nouvelles études micropaléontologiques sur le stratotype de la limite Campanien- Maastrichtien à Tercis (SO France) : compléments sur les ostracodes extraits par acétolyse.- Une nouvelle étude de la microfaune, obtenue par acétolyse des niveaux indurés dans le Campanien- Maastrichtien de la carrière de Tercis, a permis de récolter 22 espèces additionnelles au regard de l'étude publiée en 2001 et de porter ainsi à 75 espèces, réparties sur 34 genres reconnus et 4 indéterminés, la biodiversité en ostracodes de ce site. Des espèces de petite taille, généralement rares, rapportées aux genres Aversovalva, Bythoceratina et Eucytherura ont par ailleurs été recueillies. Les associations de genres et d'espèces d'ostracodes sont caractéristiques du Campanien-Maastrichtien, dans un environnement de plate-forme carbonatée ouverte. Mots-Clefs : Ostracodes ; Campanien ; Maastrichtien ; stratotype ; Tercis ; Aquitaine ; France ; acétolyse. 1. Introduction of the Tercis series (Figs. 2-3) would be profitable. In 2001 the study of microfossils, The stratotype section of the Campanian- with the exception of the investigation by thin Maastrichtian boundary at Tercis (Landes, section of planktonic foraminifera, was France) was accepted in 2001 (ODIN & restricted to the easily disaggregated levels: LAMAURELLE, 2001) following an extensive those richest in clay. At Tercis, the clay content integrated study (ODIN, 2001a) including the of these levels reached a maximum of 15 % documentation of 18 fossil groups illustrated in (ODIN, 2001c). However, from the the second work and later in ODIN et alii (2006). environmental point of view, these levels This well-known section (Fig. 1) was an indicate an input of detritus which could appropriate choice for the better establishment influence the development of micro-organisms. of the palaeobiodiversity of Upper Cretaceous The practical selection of the more clayish deposits, at a time when dinosaurs were the top levels might have discriminated those of the biological pyramid just before the organisms more tolerant to this detrital input Cretaceous-Palaeogene global crisis. and eliminated those requiring clean waters. Among the possible ways to arrive at a This was why we attempted to dissociate rocks better knowledge, it was suspected that an using more or less concentrated acetic acid at intensive study directed particularly at the different temperatures. indurated strata comprising the larger portion 1 LMTG, Université Toulouse III, CNRS, IRD, OMP, 14 avenue Édouard Belin, F-31400 Toulouse (France) [email protected] 2 Corresponding author: Université Pierre et Marie Curie, Unité de Géochronologie et Sédimentologie Océanique; Géologie Sédimentaire, Case 119, 4, Place Jussieu, F75252, Paris Cedex 05 (France) [email protected] URL: http://www-sst.unil.ch/research/meta/GSO/ Manuscript submitted July 18, 2007, accepted December 12, online since February 4, 2008 1 Carnets de Géologie / Notebooks on Geology - Article 2008/02 (CG2008_A02) Figure 1: Aerial view of the geological site at Tercis (southern Aquitaine). North is located toward the top; strata are vertical; the Campanian levels are in the South followed to the North by those of the Maastrichtian, then the Danian. The quarry front, to the East/right, is made up of 5 platforms, 170 m wide, perpendicular to the strata, and moved along 400 m during quarrying (picture G.S.O., February 1997). We obtained a satisfying disaggregation of to a guide event selected by convention (ODIN, the hard rocks in most of the levels 2001b; ODIN & LAMAURELLE, 2001). The homo- investigated. Picking of the several size geneous lithology of the section is shown on fractions of the resulting sands led to the Figure 4 which identifies 3 units. The d'Avezac obtention of new forms of previously inves- Unit is a series of limestones of which the 5 tigated fossil groups as well as to the discovery sub-units (A1 to A5) are distinguished of a number of previously unknown forms: according to their respective content of glau- microproblematica apparently needing clean cony (glaucony: facies as opposed to waters (ODIN & LETHIERS, 2006; ODIN, 2007; glauconite: mineral according to ODIN & MATTER, ODIN et alii, 2007). Bryozoans, holothurian, 1981) that alternates between very low and crinoid and ophiuroid remains, benthic and high. The Les Vignes Unit uncludes a sub-unit planktonic foraminifera, ... will be studied later, with light flint (V1) below and a sub-unit with we hope. The present work reports only the dark flint (V2) above. The lithological column information obtained concerning ostracodes: indicates the presence of glaucony (dotted) and previously unreported taxa of these microfossils of flint; flints are commonly concentrated in were found and the distribution of known forms levels of dm thickness with a metric periodicity. was made more nearly exhaustive. The numerical ages are suggested according to 1- magnetostratigraphic and biostratigraphic 2. Frame of the study correlations with radiometrically dated bentonite levels in the United States (LEWY & 2.1. Geological section ODIN, 2001), 2- a uniformity in the rate of The stratotype section of the Campanian- sedimentation is supported by the measurable Maastrichtian boundary is defined in the Grande (metric) periodicity of the deposits (orbital in Carrière at Tercis which was quarried until origin), 3- the combination of this consistency 1997. Tercis is located in the Landes near Dax, with the examination (presence, abundance, in southern Aquitaine, France, about 10 km and crystallinity) of glauconitic minerals (ODIN north of the first North Pyrenean Thrusts & AMOROSI, 2001). The age of the boundary (ROCHER, 2001). A continuous section about 200 suggested in 2001 is improved in accordance m thick was described (ODIN & ODIN, 1994). It with recently established Europe-America is 8 Ma of deposits bracketing the Campanian- correlations using inoceramids (ODIN & Maastrichtian boundary which is conventionally WALASZCZYK, 2003). The ages indicated along- sited at level 115.2 in accordance with an side the column are estimates based on original approach: this convention involves the acceptance of 71.6 Ma as the date of the use of a combination of 12 biostratigraphical boundary with an uncertainty of ±0.6 Ma signals pertaining to 6 fossil groups contiguous (confidence level 95 %). 2 Carnets de Géologie / Notebooks on Geology - Article 2008/02 (CG2008_A02) Figure 2: View of platform II, levels 5 to 30, the main outcrop of the Tercis geological site (southern Aquitaine). Carbonate strata are vertical (level 20.0 shown) with a few decimeter-thick marly horizons (picture G.S.O., July 1992). Figure 3 : View of platform III, levels 95 to 120, of the main section of the geological site at Tercis (southern Aquitaine). The Campanian-Maastrichtian boundary is shown (green). The flint-bearing strata display marls with low clay content near levels 97 and 118 (picture G.S.O., July 1992). in Europe have also been found in North 2.2. Previous results America and on the southern margin of the Figure 4 summarizes the quantitative results Mediterranean. The